The invention relates to a method for improving the fertilizing capability of sperm cells.
The effects of Hexe2x80x94Ne laser irradiation on various aspects of cell metabolism have been recognized in recent years. Extensive literature exists on the application of low-power laser irradiation in various biological systems. The therapeutic effects of laser irradiation are usually attributed to the laser parameters, i.e. wavelength, intensity, coherency, polarization or monochromaticity of the light.
Cohen et al. Photochemistry and Photobiology, 1998, 68 (3), pp. 407-413 describes that irradiation of mouse spermatozoa with a 630 nm Helium Neon laser enhances their fertilizing potential. Breitbart et al. reported in the Annual Meeting of the French Andrology Society, held at Issy-les-Moulinaux on Dec. 6 to 8, 1999, that irradiation of human sperm with a low energy Hexe2x80x94Ne laser improves the ability of poor quality sperm to penetrate egg cells.
The present invention is based on the surprising finding that the positive effect of Hexe2x80x94Ne laser on sperm fertilizing capability, described by Cohen et al. and Breitbart et al, may also be achieved by any other light source having wavelengths ranging from about 300 to about 1000 nm. Light whose wavelength is in the above range will be referred to hereinafter as xe2x80x98light in the extended visible rangexe2x80x99. Light having wavelengths between 1000 and about 2000 nm is less efficient, and in any case is hannless to the cells. Therefore, a light source emitting light with a spectrum between, for instance, 600 to 2000 nm may also be used according to the invention.
Thus, the invention provides a method for improving the fertilizing capability of sperm cells by irradiating them with light in the extended visible range, having an intensity of 1 to 1000 mW/cm2, provided that this light is not a Hexe2x80x94Ne laser light. Preferably the light intensity is between 10 and 500 mW/cm2, and more preferably between 40 and 100 mW/cm2. The inventors found out that when only UVA light (i.e. light in the range from 300 to 400 nm) is used, an intensity of about 2 mW/cm2 is preferable and when light in the range of 400 to 800 nm is used, 40 mW/cm2 intensity is most preferable. The preferable intensity of light of the full extended visible spectral range may be roughly evaluated according to the spectrum of the light source, although the most preferable intensity is to be determined experimentally.
Preferably, the light irradiation should last for 0.5 to 10 minutes, more preferably between 2 and 5 minutes. In particular, the light irradiated on the sperm cells in accordance with the present invention may be any non-laser light, be it monochromatic or polychromatic, polarized or non-polarized, coherent or incoherent. Polychromatic in this sense may be any light having a spectrum broader than 5 nm, preferably broader than 20 nm. In particular, polychromatic light having a spectral breadth covering all the visible range, and possibly a wider range, such as the light emitted by a halogen lamp, may be implemented in the method of the invention. Another non-limiting example of a light source that may be used for the light irradiation in accordance with the invention is a light-emitting diode.
The method of the invention may also be carried out by irradiating the cells with any laser, which is not Hexe2x80x94Ne, and which emits light in the extended visible range.
The method of the invention may be implemented by irradiating the sperm cells in vitro or in vivo. In the last case, if the sperm is of a mammal the epididymis of that mammal should be irradiated.